Metal-clad switchgear assemblies are typically used to connect a plurality of electrical loads to a common electrical bus. Such assemblies are typically provided with a plurality of circuit breakers having one side connected to the common bus and the other side connected to various remote electrical loads. The circuit breakers provide electrical protection to isolate the loads during overcurrent conditions, such as an overload or short circuit condition.
The circuit breakers provided in such metal-clad switchgear assemblies are typically drawout devices which may be removed from the switchgear assembly. The circuit breaker assemblies are provided with outwardly extending line and bus contacts which are adapted to automatically engage the line and bus terminals in the metal-clad switchgear assembly when the circuit breaker assembly is inserted into a cell or compartment in the metal-clad switchgear assembly.
Occasionally it is necessary to service the bus structure within the metal-clad switchgear assembly. In such situations, a circuit breaker assembly is removed from the metal-clad switchgear assembly and replaced with a ground switch assembly. The ground switch assembly allows either the line or bus terminals to be grounded during maintenance for personnel safety. Prior to grounding the line or bus terminals within the metal-clad switchgear assembly, it is customary to disconnect the upstream source of electrical power supplying the switchgear assembly. However, under certain conditions, it may be desirable to ground a live circuit. Another situation arises wherein the upstream source of electrical power is inadvertently reenergized during bus maintenance prior to closing of the ground switch. In both such situations, it is necessary to prevent injury to personnel and damage to the equipment.
These dangers can be minimized by insuring that the grounding switch contacts fully close in such a situation. In some known grounding switch devices, contact assemblies are provided which contain current loops which act to increase the contact pressure once the grounding switch is fully closed but may repel the contacts due to the magnetic repulsion forces when the ground switch is being closed in on a live circuit.
It is also important to prevent the contacts from bouncing after the ground switch contacts are closed. Contact bounce results in arcing which may cause the contacts to weld together when the ground switch device is closed in on a live circuit. Once the contacts are welded together, it becomes extremely difficult to remove the grounding switch device from the metal-clad switchgear assembly because of the various mechanical interlocks which prevent the ground switch from being removed when it is in the closed position.